This invention relates to suction catheter assemblies and is more particularly concerned with assemblies of the kind having an aspirating catheter enclosed within a protective, flexible sleeve and which can be advanced through a coupling at one end of the assembly. The coupling has one port connected to a tracheal tube and two further side ports by which ventilation of the patient can take place. In use, the machine end of the catheter is connected to a suction source via a valve. Secretions that build up on the inside of the tracheal tube, the trachea and bronchi can be periodically removed by opening the valve and advancing the catheter through the coupling and down the tracheal tube. The coupling enables ventilation of the patient to continue while suctioning takes place.
One problem with this kind of assembly is that air may enter the sleeve causing it to inflate which can make subsequent use of the assembly more difficult. A small amount of air will be present in the sleeve as a result of assembly and additional air can be pulled into the sleeve during the negative pressure cycle of sterilization. Air from the ventilation system, during use, can also be forced back into the sleeve. Although a sliding seal can be provided in the coupling with the outside of the catheter, this does not provide a total air seal. Attempts to improve the seal by making it a tighter fit tend to cause an indentation in the catheter, especially when it is stored for prolonged periods or subjected to elevated temperature, such as during sterilization. One way of preventing the accumulation of air in the sleeve is to provide a small vent that allows air to escape to atmosphere. This, however, is not desirable because it can allow the escape of contaminated material from the assembly onto the user.
Examples of catheter assemblies having an aspirating catheter which is contained within a sleeve and which can be pushed through a sliding seal on a coupling are described in several patents, such as U.S. Pat. No. 3,991,762 to Radford; U.S. Pat. No. 4,569,344 to Palmer; U.S. Pat. No. 4,638,539 to Palmer; U.S. Pat. No. 4,696,296 to Palmer; U.S. Pat. No. 4,825,859 to Lambert; U.S. Pat. No. 4,834,726 to Lambert; U.S. Pat. No. 4,836,199 to Palmer; U.S. Pat. No. 4,838,255 to Lambert; U.S. Pat. No. 4,872,579 to Palmer; U.S. Pat. No. 4,938,741 to Lambert; U.S. Pat. No. 4,967,743 to Lambert; U.S. Pat. No. 4,981,466 to Lambert; U.S. Pat. No. 5,025,806 to Palmer; U.S. Pat. No. 5,029,580 to Radford; U.S. Pat. No. 5,060,646 to Page; U.S. Pat. No. 5,065,754 to Jensen; U.S. Pat. No. 5,073,164 to Hollister: and GB 2207736 to Hollister. Suction catheter assemblies of this kind are also available from Smiths Industries Medical Systems Inc under the trade mark STERICATH and from Ballard Medical Products Inc under the trade mark TRACHCARE.
Examples of venting of the sleeve in the prior art are described, for example, in U.S. Pat. No. 5,088,486 to Jinotti which discloses the sleeve provided with small venting holes for venting entrapped air from the sleeve, and U.S. Pat. No. 4,850,350 to Jackson in which the sleeve venting is accomplished through a one-way, so called "duck bill" venting valve. The Jackson venting valve is in communication with the inside of the sleeve and with the suction catheter. The one-way venting valve is adapted to open in response to the opening of the suction valve due to a negative pressure created in the catheter lumen. This V negative pressure draws the secretions from the patient's lungs and also evacuates the air from the sleeve. This, however makes maneuvering of suction catheter difficult since the negative pressure inside the sleeve forces the it onto the catheter.